1. Field
This disclosure relates to construction of structures, such as walls and buildings. This disclosure also relates to extrusion of construction material and devices and apparatus that are involved in such a process, including extrusion nozzles.
2. Description of Related Art
Constructing homes, offices, and other structures has an ancient heritage. Despite centuries of development, however, construction can still be very labor intensive. Even a modest sized structure may require the efforts of numerous workers. The appearance and quality of several structures built from the same design may also vary due to differences in the skills, efforts, supervision, and techniques employed by their builders. Construction may also waste material. When standard off-the-shelf lengths of wood is used, for example, the wood may have to be cut to meet design requirements. Construction may also be hazardous. Construction workers may be killed or seriously injured.
These problems gave rise to the nozzle assemblies disclosed in U.S. Pat. No. 7,153,454, issued Dec. 26, 2006, entitled “Multi-Nozzle Assembly for Extrusion of Wall,” as well as the related equipment and methods disclosed in the patent applications cited above.
These patent applications and patent collectively disclose equipment and methods for automatically constructing buildings by extruding construction material, layer by layer, from one or more extrusion nozzles. These nozzles may be manipulated by robots under computer control. The process has become known as “Contour Crafting.”
Such advancements have brought with them corresponding challenges. For example, it may be challenging to extrude walls which have multiple layers, such as an internal core of insulation, a stucco exterior, and a plastered interior. It may also be challenging to craft openings in such extruded walls for such components as windows and doors. It may also be challenging to create a uniform and level base layer when the underlying surface is uneven.
One particular challenge relates to controlling the flow of material extruded from a nozzle as it forms a layer. Flow rate is generally a parameter that must be regulated in a variety of situations. One example includes a situation where a substantially homogenous layer of material is to be extruded. If, when the layer is constructed, the material flow rate changes substantially, the layer will likely vary in size and shape. The potential variance may introduce unwanted hazards, weaknesses and defects and present unwanted aesthetic artifacts, and it may result in structures that are not consistent with their originally issued specifications.
Several flow measurement techniques have been proposed or implemented to address this problem. However, for certain fluids and materials these methods are either unworkable or they are too slow in providing an accurate response, particularly in automated extrusion processes.